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1. Field of the Invention
The present invention, in certain respects, relates to the field of machine vision. In other respects, the present invention relates to a method and system that aligns a geometric object model with an image.
2. Description of Background Information
Various machine vision systems perform alignment as a first step for various tasks. For example, a machine vision inspection system will identify the correct alignment of an object before the object appearing in an image is inspected. Another example is that a robot aligns its field of view before it decides the direction in which to proceed and identifies those what obstacles to avoid. Such alignment often requires training based on an image of the object to be recognized, together with, for instance, a specification of the origin of the object as well as the dimension information of the object. While such image based training for alignment can be effective, there are certain situations where it is impractical.
Training an alignment tool based on object images is tedious and time consuming. This becomes especially a problem for manufacturing processes, where there may be a wide variety of products or objects that need to be inspected using machine vision inspection. Furthermore, product designs may frequently change. Even a minor revision to an object, for example, its shape, may require retraining.
Parameterized geometric object models may be used, instead of using object images, to train machine vision inspection systems. For purposes of the disclosure herein, a geometric model of an object comprises parameter representations of the geometry of the object. For example, parameterized geometric models are created and employed in machine vision inspection systems when aligning fiducial marks on electronic components. For a simple object, its geometric model may be created by manually entering the shape and dimension information about the object. For more complicated objects, however, creating a geometric object model may be even more difficult than training using images. That is, the complexity associated with creating a geometric model for a complicated object may outweigh the advantage of using a geometric object model for training an alignment tool.
There is a need to make direct use of available geometric object models for alignment purposes in machine vision systems so that the training process can be more efficient and such trained alignment tools can effectively align a geometric object model with an image.
The present invention is provided to improve upon techniques for obtaining a geometric object model used in a machine vision application and for performing alignment with such models. Improved methods and features are presented that address the need identified above and provide methods and apparatuses for aligning an object model with an image. Aspects of the present invention can improve both the efficiency of a training phase as well as the effectiveness of an on-line alignment phase. Existing geometric object models, such as CAD models, are utilized directly but revised with respect to the needs for alignment. A revised geometric object model is constructed especially for alignment purpose. It retains only the geometric features, selected from the original geometric object model, that are considered salient and useful with respect to the underlying task of aligning a geometric object model with an image. An alignment tool can be trained based on a revised geometric object model. Both a revised geometric object model and its correspondingly trained alignment tool may be further refined using the feedback information from an on-line alignment operation so that the revised model and the corresponding alignment tool can be adjusted to better fit the real scenarios of different machine vision applications.